Extremely high frequency, EHF, is the International Telecommunications Union, ITU, designation for the band of radio frequencies in the electromagnetic spectrum from 30 to 300 gigahertz, GHz. Radio waves in this band have wavelengths from ten to one millimeter, giving it the name millimeter band or millimeter wave, sometimes abbreviated MMW or mmW.
These frequency bands are envisioned to be used as the corresponding spectrum is not as occupied as compared to frequently used frequency bands, for example frequency bands below 6 GHz, thereby improving system capacity. Propagation effects are, however, severe in these frequency bands. For example, signal quality decays quickly with distance and, for example, diffraction, penetration and/or reflection losses are considered to be high.
One of the proposed advancements in this area is to use beamforming with narrow beams and high directivity using very-large antenna arrays, namely massive Multiple-Input-Multiple-Output, MIMO, antennas.
Beamforming or spatial filtering is a signal processing technique used in arrays for directional signal transmission or reception. This is achieved by combining elements in an antenna array in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity. The improvement compared with omnidirectional reception/transmission is known as the directivity of the array.
Following the above, it may be advantageous if measurement and reporting of multiple narrow beams, or simply put beam management, is efficiently addresses so that access nodes, AN's, are able to, for example, keep the signal quality experienced on the user side, i.e. at the User Equipment, UE, above a predetermined threshold.
It is noted that for the next generation of radio technology, namely 5G new radio, NR, 3GPP briefly describes a set of procedures to beam management indicating that the procedure to intra/inter AN's beam switch can use a smaller set of beams compared to the joint beam space.
In Long Term Evolution, LTE, neither massive MIMO antennas nor mm-Wave bands are supported. Thus, the LTE solution only supports the management of the entire beam space. The use of such a solution to manage several narrow beams would prohibitively increase the signalling burden.
Currently deployed solutions are based on beam training. That is, the beams, or the set of beams, to be used for transmission is determined based on UE measurements on previously selected beams. These measurement may, for example, be out-of-date and this can cause a spatial misalignment that may lead to beam failure.